MUWIC Newsletter - June 2005

(Issued: June 2, 2005)

 

Millersville University Weather Information Center (MUWIC)

Eric J. Horst, Director

 

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LEAD STORY: “4th Coolest May on Record”

 

May is commonly recognized for producing the first extended spell of summer-like heat and humidity, often just in time for the Memorial Day weekend. This generalization was a bust this year, as May panned out to be the coolest in more than thirty years across the Northeast. Locally, the average monthly temperature averaged 4 degrees below normal—this ranks as the 4th coolest on record.

 

Unusually persistent jet stream blocking is to blame for the ongoing chill and occasional late-Spring frosts. A large area of high pressure developed from Hudson Bay to near Greenland, thus, allowing a series of disturbances to repeatedly cutoff, or stall, south of this block near New England. The resultant northwest wind flow across Pennsylvania yielded many below normal days (22) and very little meaningful rainfall. In fact, rainfall for the month totaled just 1.14 inches, making for the driest May in over a decade.

 

So, what does a cool, dry May portend for the summer ahead? Analysis of our 90-year climatological database provides few solid analogs to leverage. However, eight similarly dry Mays were all followed by summers that produce normal to above normal temperatures. Therefore, there is a weak signal for a warmer-than-normal summer ahead.

 

Top 5 Coolest Mays (departure from normal)*

  1. 1917 (-6.3 F)
  2. 1967 (-5.2 F)
  3. 1968 (-4.7 F)
  4. 2005 (-4.0 F)
  5. 1973 (-3.9 F)

 

* - Based on 90-year Millersville/Lancaster database.

 

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EVENT OF THE MONTH

 

May 25th was a damp, cloudy, and cool day of dramatic proportions. The high temperature of 56 degrees was a remarkable 21 degrees below normal for the date. But it could have been worse; snow showers were reported in the White Mountains of New Hampshire!

 

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STAT OF THE MONTH

 

What a difference a year makes. May 2004 was the warmest on record here in Lancaster as temperatures averaged 6.9 degrees above normal. May 2005 concluded 4.0 degrees below normal—the 4th coolest on record.

 

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MAY CLIMATOLOGY (MU Weather Station)

 

Average High Temp: 69.5 F

Average Low Temp: 46.4 F                                                   

Average Monthly Temp: 58.0 F                                          

(Departure from Normal: -4.0 F)

                  

Precipitation: 1.14 inches  

(Departure from Normal: -2.48)   

Annual Precipitation: 13.74 inches              

(Departure from Normal: -2.21)

 

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JUNE NORMALS, RECORDS & FACTS

 

Normal high/low temperatures range from 80/54 on June 1st to 85/61 by month’s end. The record high for June is 103 degrees set on the 20th of 1923 and 29th of 1934. The lowest temperature recorded in June is 33 F set on the 5th of 1921 and the 8th of 1932. Normal liquid precipitation for the month is 3.88 inches. The rainiest June on record (14.14 inches) occurred in 1972 when the remains of Hurricane Agnes moved through the region. The driest June was in 1966 when only 0.54 inches fell. Summer officially begins on June 21st at 2:46 a.m.

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JUNE OUTLOOK

 

After a remarkably chilly month, June is beginning on a more seasonable note as the upper-level flow pattern evolves into a more zonal configuration. In fact, several medium-range models are forecasting a trough to develop over the western US (in the mean). This would result in increased ridging over the eastern US and a good chance of a period of above normal conditions towards mid-month.

 

Precipitation-wise, the increasing heat and humidity provides a more favorable environment for the formation of afternoon showers and thunderstorms. While I do not see any signs of an especially rainy pattern, I do expect that June will yield more total rainfall than we received in May (1.14”). As summer progresses, we’ll also need to keep an eye on the tropics. Remnants of tropical storms and hurricanes can produce tremendous rainfall in our area, although many summers we receive no such rainfall from tropical systems.

 

In the end, I expect June will conclude with above normal temperatures and normal to below normal precipitation.

 

COPYRIGHT 2005 Millersville University

 

Published monthly by the Millersville University Weather Information Center.

Subscribe on our homepage at www.atmos.millersville.edu/~wic

 

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